{"id":1736,"date":"2016-10-09T15:56:01","date_gmt":"2016-10-09T07:56:01","guid":{"rendered":"https:\/\/ai.zhousir.top\/?p=1736"},"modified":"2026-08-18T12:09:36","modified_gmt":"2026-08-18T04:09:36","slug":"hashmap%e7%9a%84%e5%b7%a5%e4%bd%9c%e5%8e%9f%e7%90%86","status":"publish","type":"post","link":"https:\/\/ai.zhousir.top\/?p=1736","title":{"rendered":"HashMap\u7684\u5de5\u4f5c\u539f\u7406"},"content":{"rendered":"
\n

\u9762\u8bd5\u5e38\u4ece\u201c\u4f60\u7528\u8fc7 HashMap \u5417\uff1f\u4ec0\u4e48\u662f HashMap\uff1f\u4e3a\u4ec0\u4e48\u7528\u5b83\uff1f\u201d\u95ee\u8d77\u3002\u591a\u6570\u4eba\u4f1a\u7b54\uff1a\u662f\u7684\uff0c\u7136\u540e\u5217\u51fa\u7279\u6027\u2014\u2014HashMap \u53ef\u4ee5\u63a5\u53d7 null \u952e\u548c\u503c\uff0cHashtable \u4e0d\u884c<\/strong>\uff1bHashMap \u975e synchronized<\/strong>\uff1bHashMap \u5f88\u5feb<\/strong>\uff1b\u5b58\u7684\u662f\u952e\u503c\u5bf9<\/strong>\u3002\u8fd9\u53ea\u80fd\u8bf4\u660e\u4f60\u7528\u8fc7\u5b83\u3002\u63a5\u4e0b\u6765\u9762\u8bd5\u5b98\u4f1a\u5f80\u539f\u7406\u4e0a\u8ffd\u3002<\/p>\n

\u201c\u4f60\u77e5\u9053 HashMap \u7684\u5de5\u4f5c\u539f\u7406\u5417\uff1fget() \u600e\u4e48\u5de5\u4f5c\uff1f\u201d\u6709\u4eba\u4f1a\u8bf4\u53bb\u770b\u6e90\u7801\u6216 Google\u3002\u80fd\u7b54\u5230\u70b9\u5b50\u4e0a\u7684\u4eba\u4f1a\u8bf4\uff1aHashMap \u57fa\u4e8e hashing<\/strong>\uff0c\u7528 put(key, value)<\/code> \u5b58\u3001get(key)<\/code> \u53d6\u3002\u8c03\u7528 put \u65f6\u5148\u5bf9\u952e\u505a hashCode()<\/code>\uff0c\u7528\u8fd4\u56de\u503c\u5b9a\u4f4d bucket\uff0c\u518d\u628a Entry\uff08\u952e\u5bf9\u8c61+\u503c\u5bf9\u8c61\uff09<\/strong> \u653e\u8fdb\u53bb\u3002\u5173\u952e\u70b9\u662f bucket \u91cc\u5b58\u7684\u662f Map.Entry<\/code>\uff0c\u4e0d\u662f\u53ea\u5b58 value\u2014\u2014\u5426\u5219\u540e\u9762\u201c\u600e\u4e48\u53d6\u51fa\u5bf9\u8c61\u201d\u6839\u672c\u8bb2\u4e0d\u6e05\u3002<\/p>\n

\u4e00\u3001hashCode \u76f8\u540c\uff1a\u78b0\u649e<\/h2>\n

\u201c\u4e24\u4e2a\u5bf9\u8c61 hashcode \u76f8\u540c\u4f1a\u53d1\u751f\u4ec0\u4e48\uff1f\u201d\u6709\u4eba\u4f1a\u8bef\u4ee5\u4e3a\u5bf9\u8c61\u76f8\u7b49\u3001HashMap \u629b\u5f02\u5e38\u6216\u4e0d\u5b58\u3002\u9762\u8bd5\u5b98\u4f1a\u63d0\u9192\uff1aequals()<\/code> \u548c hashCode()<\/code> \u662f\u4e24\u56de\u4e8b\uff0chashcode \u76f8\u540c\u4e5f\u53ef\u4ee5\u4e0d\u76f8\u7b49\u3002\u7ee7\u7eed\u7b54\uff1abucket \u4f4d\u7f6e\u76f8\u540c\uff0c\u53d1\u751f\u78b0\u649e<\/strong>\u3002HashMap \u7528\u94fe\u8868\u5b58\u5bf9\u8c61\uff0c\u8fd9\u4e2a Entry \u4f1a\u6302\u5230\u94fe\u8868\u4e0a\u3002\u5904\u7406\u78b0\u649e\u7684\u65b9\u6cd5\u5f88\u591a\uff0c\u94fe\u8868\u662f\u6700\u7b80\u5355\u7684\u4e00\u79cd\uff0c\u4e5f\u6b63\u662f\uff08Java 7 \u53ca\u66f4\u65e9\uff09HashMap \u7684\u505a\u6cd5\u3002<\/p>\n

\u201c\u4e24\u4e2a\u952e hashcode \u76f8\u540c\uff0c\u5982\u4f55\u83b7\u53d6\u503c\u5bf9\u8c61\uff1f\u201d\u5148\u7528\u952e\u7684 hashcode \u627e\u5230 bucket\uff0c\u518d\u904d\u5386\u94fe\u8868<\/strong>\u3002\u9762\u8bd5\u5b98\u4f1a\u8ffd\u95ee\uff1a\u4f60\u6ca1\u6709\u503c\u5bf9\u8c61\u53ef\u6bd4\u8f83\uff0c\u600e\u4e48\u786e\u5b9a\u627e\u5230\u4e86\uff1f\u9664\u975e\u4f60\u77e5\u9053\u94fe\u8868\u8282\u70b9\u91cc\u662f\u952e\u503c\u5bf9\uff0c\u5426\u5219\u7b54\u4e0d\u4e0a\u3002\u8bb0\u4f4f\u8fd9\u4e00\u70b9\u7684\u4eba\u4f1a\u8bf4\uff1a\u627e\u5230 bucket \u540e\u8c03\u7528 keys.equals()<\/code> \u627e\u5230\u6b63\u786e\u8282\u70b9\uff0c\u518d\u53d6 value\u3002\u5b8c\u7f8e\u7b54\u6848\u3002<\/p>\n

\u5f88\u591a\u4eba\u5728\u8fd9\u4e00\u73af\u628a hashCode()<\/code> \u548c equals()<\/code> \u641e\u6df7\uff1ahashCode \u4e00\u8def\u51fa\u573a\uff0cequals \u53ea\u5728\u53d6 value \u65f6\u51fa\u73b0\u3002\u4f18\u79c0\u5f00\u53d1\u8005\u8fd8\u4f1a\u8865\u5145\uff1a\u952e\u7528\u4e0d\u53ef\u53d8\u3001final \u5bf9\u8c61\uff0c\u5e76\u6b63\u786e\u5b9e\u73b0 equals\/hashCode\uff0c\u80fd\u51cf\u5c11\u78b0\u649e\u3001\u63d0\u9ad8\u6548\u7387\u3002\u4e0d\u53ef\u53d8\u6027\u8ba9 hashcode \u53ef\u7f13\u5b58\uff0cString<\/code>\u3001Integer<\/code> \u8fd9\u7c7b\u5305\u88c5\u7c7b\u5f53\u952e\u5f88\u5408\u9002\u3002<\/p>\n

\u4e8c\u3001\u8d1f\u8f7d\u56e0\u5b50\u4e0e\u6269\u5bb9<\/h2>\n

\u201cHashMap \u5927\u5c0f\u8d85\u8fc7\u8d1f\u8f7d\u56e0\u5b50\uff08load factor\uff09\u5b9a\u4e49\u7684\u5bb9\u91cf\u600e\u4e48\u529e\uff1f\u201d\u9ed8\u8ba4\u8d1f\u8f7d\u56e0\u5b50\u662f 0.75<\/strong>\uff1abucket \u586b\u5230 75% \u65f6\uff0c\u4f1a\u521b\u5efa\u539f\u6765\u4e24\u500d\u5927\u5c0f\u7684 bucket \u6570\u7ec4\uff0c\u628a\u65e7\u5bf9\u8c61\u653e\u8fdb\u53bb\u3002\u8fd9\u4e2a\u8fc7\u7a0b\u53eb rehashing<\/strong>\uff0c\u56e0\u4e3a\u8981\u518d\u8c03 hash \u627e\u65b0\u4f4d\u7f6e\u3002<\/p>\n

\u201c\u91cd\u65b0\u8c03\u6574\u5927\u5c0f\u6709\u4ec0\u4e48\u95ee\u9898\uff1f\u201d\u591a\u7ebf\u7a0b\u4e0b\u53ef\u80fd\u4ea7\u751f\u6761\u4ef6\u7ade\u4e89\uff08race condition\uff09\u3002\u4e24\u4e2a\u7ebf\u7a0b\u540c\u65f6\u53d1\u73b0\u9700\u8981\u6269\u5bb9\uff0c\u4f1a\u4e00\u8d77\u8c03\u6574\u3002\u79fb\u52a8\u5230\u65b0 bucket \u65f6\uff0cHashMap \u628a\u5143\u7d20\u653e\u5728\u94fe\u8868\u5934\u90e8<\/strong>\u800c\u4e0d\u662f\u5c3e\u90e8\uff08\u907f\u514d\u5c3e\u90e8\u904d\u5386\uff09\uff0c\u94fe\u8868\u6b21\u5e8f\u4f1a\u53cd\u8fc7\u6765\u3002\u6761\u4ef6\u7ade\u4e89\u4e00\u65e6\u53d1\u751f\uff0c\u53ef\u80fd\u6b7b\u5faa\u73af\u3002\u8fd9\u65f6\u53ef\u4ee5\u53cd\u95ee\uff1a\u4e3a\u4ec0\u4e48\u8981\u5728\u591a\u7ebf\u7a0b\u91cc\u7528 HashMap\uff1f<\/p>\n\n\n\n\n\n\n\n\n\n
\u95ee\u9898<\/th>\n\u8981\u70b9<\/th>\n<\/tr>\n<\/thead>\n
put \/ get<\/td>\nhashCode \u5b9a\u4f4d bucket\uff0cEntry \u5b58\u952e\u503c\u5bf9<\/td>\n<\/tr>\n
\u78b0\u649e<\/td>\n\u540c\u4e00 bucket \u7528\u94fe\u8868\uff08Java 8 \u8d77\u957f\u94fe\u4f1a\u8f6c\u7ea2\u9ed1\u6811\uff09<\/td>\n<\/tr>\n
\u53d6 value<\/td>\nbucket \u5185\u7528 key.equals() \u627e\u5230\u8282\u70b9<\/td>\n<\/tr>\n
\u8d1f\u8f7d\u56e0\u5b50<\/td>\n\u9ed8\u8ba4 0.75\uff0c\u8d85\u4e86\u6269\u5bb9\u4e3a\u7ea6 2 \u500d\u5e76 rehash<\/td>\n<\/tr>\n
\u591a\u7ebf\u7a0b\u6269\u5bb9<\/td>\n\u94fe\u8868\u5934\u63d2\u53ef\u80fd\u5bfc\u81f4\u6b7b\u5faa\u73af\uff0c\u6539\u7528 ConcurrentHashMap<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u4e09\u3001\u952e\u7684\u9009\u62e9\u4e0e ConcurrentHashMap<\/h2>\n

\u4e3a\u4ec0\u4e48 String\u3001Integer \u9002\u5408\u5f53\u952e\uff1f<\/strong> \u5b83\u4eec\u4e0d\u53ef\u53d8\u3001final\uff0c\u5df2\u91cd\u5199 equals \u548c hashCode\u3002\u4e0d\u53ef\u53d8\u6027\u5fc5\u8981\uff1a\u8ba1\u7b97 hashCode \u65f6\u952e\u4e0d\u80fd\u53d8\uff0c\u5426\u5219\u653e\u5165\u548c\u53d6\u51fa\u65f6 hash \u4e0d\u540c\uff0c\u5c31\u627e\u4e0d\u5230\u5bf9\u8c61\u3002\u4e0d\u53ef\u53d8\u8fd8\u6709\u7ebf\u7a0b\u5b89\u5168\u7b49\u597d\u5904\u3002\u4e24\u4e2a\u4e0d\u76f8\u7b49\u7684\u5bf9\u8c61\u82e5\u8fd4\u56de\u4e0d\u540c hashcode\uff0c\u78b0\u649e\u66f4\u5c11\uff0c\u6027\u80fd\u66f4\u597d\u3002<\/p>\n

\u53ef\u4ee5\u7528\u81ea\u5b9a\u4e49\u5bf9\u8c61\u5f53\u952e\u5417\uff1f<\/strong> \u53ef\u4ee5\uff0c\u53ea\u8981\u9075\u5b88 equals\/hashCode \u7ea6\u5b9a\uff0c\u5e76\u4e14\u63d2\u5165 Map \u540e\u4e0d\u518d\u6539\u53d8\u3002\u81ea\u5b9a\u4e49\u5bf9\u8c61\u82e5\u4e0d\u53ef\u53d8\uff0c\u521b\u5efa\u540e\u5c31\u4e0d\u80fd\u6539\uff0c\u5df2\u7ecf\u6ee1\u8db3\u5f53\u952e\u7684\u6761\u4ef6\u3002<\/p>\n

\u80fd\u7528 ConcurrentHashMap \u4ee3\u66ff Hashtable \u5417\uff1f<\/strong> Hashtable \u6574\u8868 synchronized\uff1bConcurrentHashMap \u53ea\u9501\u4e00\u90e8\u5206\uff08\u5206\u6bb5\u6216\u6876\uff09\uff0c\u540c\u6b65\u6027\u80fd\u66f4\u597d\u3002\u53ef\u4ee5\u4ee3\u66ff Hashtable\uff0c\u4f46 Hashtable \u63d0\u4f9b\u66f4\u5f3a\u7684\u6574\u8868\u4e92\u65a5\u3002\u8be6\u89c1 \u8fd9\u7bc7\u535a\u5ba2<\/a>\u3002<\/p>\n

\u56db\u3001\u8fd9\u4e9b\u95ee\u9898\u8986\u76d6\u54ea\u4e9b\u77e5\u8bc6\u70b9<\/h2>\n